In a thermo/hydraulic free-piston engine, the stroke of the piston is used directly to produce hydraulic energy. For every stroke of the piston, a predetermined volume of fluid is delivered from the free-piston engine. Consequently, the pressurized fluid being delivered to the work system is being delivered in pulses. It is well known to use accumulators to store the pressurized fluid so that a steady pressure level can be delivered to the work system. Since the thermo/hydraulic free-piston engine is not continuously ran, the accumulators must store the pressurized fluid up to a maximum limit and cause the thermo/hydraulic free-piston engine to shut off and once the pressure level in the accumulators has reduced to some minimum level the thermo/hydraulic free-piston engine is restarted. In order to keep the accumulators at their maximum pressure level, extra energy from a power source is needed. Actuators in a work system are normally operated to manipulate a load/weight or inertia load of varying capacities. As is well known, when the load is small, the system does not need high pressure to move the load. It would be beneficial to provide the needed volume of fluid at a lower pressure level to move the load. Likewise, when a load is being lowered or the direction of the load is being changed, the volume of fluid being exhausted from the actuator is pressurized and the energy thereof is wasted by allowing the pressurized volume of fluid to be exhausted to the reservoir. At times and under certain conditions, it would be beneficial to use the volume of pressurized fluid to supplement the flow into the actuator or to amplify the pressure of the fluid to recharge the accumulators without having to use energy from the free-piston engine. It would also be beneficial in systems having other sources of pressurized fluid to supplement the pressure in order to keep the main source from being used any more than necessary.
The present invention is directed to overcoming one or more of the problems as set forth above.